The Rhyme And Reason Behind The Company’s Success In The Diesel Industry

Whether you’re looking for more power, need to replace a dead VGT, or want a budget-friendly bolt-on, BorgWarner has long offered the lion’s share of fixed geometry turbo options in the diesel aftermarket. For every application, from Cummins to Duramax to Power Stroke, and from stock to four-digit horsepower, not only is there a BorgWarner that fits the bill, but one that performs. No other turbo manufacturer offers a product line as comprehensive as Borg’s, or as many configurations. Ample options provide the end-user the ability to spec the perfect off-the-shelf turbocharger for their specific needs.

Beyond their performance potential, BorgWarner turbos have long enjoyed a reputation for durability. Its units are capable of surviving 50, 60, even 70 psi of boost in a single turbo application, and on a regular basis. Couple that toughness with affordability and high availability and you get a very popular product. It’s why, for two decades, BorgWarner turbochargers have been the preferred choice in the diesel industry. In the pages that follow, we’ll highlight some of the most popular BorgWarner turbos in the diesel world: its S300 and S400 frame units. They’re proven, reliable, efficient, highly configurable, and arguably provide the best bang for the buck in turbochargers. Here’s why.

The specific niche under the BorgWarner umbrella that most pertains to the diesel performance industry is the AirWerks division. In 2002, the aftermarket group at BorgWarner Turbo Systems started the AirWerks program. The independent program was created to assist the needs of BorgWarner distributors who sell turbos to the competitive motorsports market. It was also created to help customers who were looking to get a little more performance out of their factory turbocharged car or truck.
Without a doubt, BorgWarner turbochargers earned their stripes in the diesel industry aboard 5.9L Cummins-powered trucks—the platform most hardcore enthusiasts were working with back around the turn of the century. In time, the BorgWarner love would spread to the V-8 offerings (Duramax and then Power Stroke), but in the beginning it was the Cummins crowd that unofficially performed the majority of the R&D for the diesel segment.
One area where BorgWarner turbochargers can be confusing for newcomers is in their terminology—or more accurately, the aftermarket’s adopted terminology. As an example, in the diesel world the label “S366” or “S480” is thrown around quite a bit, even though it leaves much to be desired (notice the S300 over S400 compound arrangement on the 12-valve Cummins pictured here). The former example means that the turbo is an S300 frame and utilizes a compressor wheel with a 66mm inducer. It provides no insight as to the turbine wheel size, the A/R of the exhaust housing, or whether it’s an SX3 or an SX-E. The correct nomenclature from AirWerks would look like this for PN 177275 (a cast wheel S366): S300SX3 66/80 .91. Translation: S300SX3 line, 66mm compressor wheel inducer, 80mm turbine wheel inducer, .91 A/R exhaust housing. For whatever reason (possibly to keep things shorthand), most enthusiasts stick to the simplistic S366 (or S467.7, S472, S480, etc.) labeling.
It’s not on every BorgWarner turbo you’ll find, but it is on the majority of the units found throughout the diesel pickup industry. It’s called twin-scroll turbine housing technology and BorgWarner uses it to produce quicker spool up by dividing exhaust flow. Exhaust gases leaving the engine are routed into so-called scrolls (spirals) and then reunited at the turbine wheel. This technology is nothing new and certainly not unique to BorgWarner, but it pays off big in the drivability department. Compared to an open scroll (or non-divided turbine inlet), target boost pressure can be achieved as quick as 1,000 rpm sooner—and in a low-revving diesel, 1,000 rpm is a big deal.
To be sure, BorgWarner didn’t invent twin-scroll technology, but they have arguably perfected it, and utilize it across much of the S300 and S400 product lines. Key benefits of a twin-scroll turbine housing other than improving low-rpm boost are that it increases low-rpm torque, improves fuel economy, reduces engine pumping losses, maximizes turbine efficiency, and lowers exhaust gas temperature.
BorgWarner’s forged milled compressor wheels (called FMW for short) all but killed off the aftermarket “billet” wheel craze that once held a lot of sway in the diesel industry. An off-the-shelf FMW can outperform most aftermarket compressor wheels (not all), which makes selling a complete, fully balanced, box turbo an easy sell. Being made from forged-aluminum also makes it stronger than most aftermarket billet-aluminum wheels. And when compared to the average cast-aluminum wheel, BorgWarner claims its FMW wheels are 213-percent stronger.
All of BorgWarner’s compressor wheels are designed using computer software that develops a three-dimensional calculation of the airflow and pressure. Full disclosure: the company’s cast compressor wheels work extremely well. However, its FMW versions changed the game. Compressor efficiency is also very good, higher than 70-percent on most sections of the compressor map, and quality checks such as X-raying are performed on each wheel to ensure every unit leaves the production line fit for a long service life.
Extended tip technology is also a big part of the success of BorgWarner’s compressor wheels. This technology enables quicker spool-up at low engine speed without sacrificing top-end flow (i.e. the turbo acts like a bigger unit at high rpm, but a smaller one at low rpm). Picture a 72mm compressor wheel that flows what a 76mm wheel can, but performs like a 67mm at low engine speed. This is the benefit that extended tip technology affords you.
Despite the glamor associated with the ball-bearing center cartridges employed on some turbos, BorgWarner’s twin hydrodynamic journal bearings have proven highly robust, even with excessive shaft speed in the mix. One high mark of the use of journal bearings is that the center sections of S300 and S400 frame chargers are fully serviceable and won’t break the bank—which is often not the case with ball-bearing turbochargers. The option to upgrade to a 360-degree thrust bearing assembly is also offered on most BorgWarner S300 and S400’s, adding tremendous insurance in high drive pressure and shaft speed applications. A 360 thrust upgrade typically runs just $120 to $180.
Various exhaust housing options are offered for each BorgWarner model, which makes it possible to fine-tune your drivability (spool up), top-end performance, and mid-range to your liking. On S400SX models alone there are eight different housings to choose from
The ability to adjust the compressor housing orientation on both S300 and S400 turbos makes them flexible enough to accommodate virtually any hot-side intercooler piping. The same goes for the exhaust housing, which can be clocked to work with any exhaust manifold (I-6) or exhaust collector (V-8) you choose.
For the money, there is tremendous value in the S300 and S400 game. Take an S369 SX-E for example. It’s a charger that flows 98 lbs/min (1,400 cfm) thanks to its FMW compressor but when spec’d with a standard (and common) T4 divided exhaust housing (.91 or 1.00 A/R) retails for just over $1,000 to $1,050 (through Pure Diesel Power, for example). For tighter budgets and lower horsepower builds, the old-school, cast-wheel S300SX3 line is still around—and the 66mm S366 shown here will only run you a touch over $750 through XDP.
The equally popular box FMW S467.7 retails between $1,300 and $1,350 ($1,333 at Summit Racing) and can support north of 700-rwhp in any application while also providing solid drivability characteristics. Small to mid-size S400 frame chargers (with 67mm to 82mm compressor wheels and T4 exhaust housings) typically use BorgWarner’s 74/83mm turbine (exducer/inducer) or 81/87mm turbine, while larger versions (including SX-E models, with T6 exhaust housings) utilize the 82/92mm or 88/96mm turbine.
A T6 S475 with the large 96mm turbine wheel inside a 1.32 A/R exhaust housing—a good candidate as an atmosphere charger in a smaller set of compounds—can be had for just $627 and change from Scheid Diesel. We’ve even seen this turbo support nearly 800-rwhp in S300/S475 arrangements, primarily on 5.9L common-rails, but we’ve also seen it employed as an atmosphere charger on our fair share of highly drivable, 750-plus hp Duramax’s.
Years ago, an S480 was typically reserved for a compound turbo setup and left in T6 form. Today however, with improvements in compressor technology, cylinder head flow, and engine tuning, these massive chargers have been successfully campaigned as big singles. Some are fitted with a T4 exhaust housing to work, while others rely on a loose converter to bring a T6 version to life in a respectable manner. In SX-E form, the S480 SX-E FMW compressor wheel flows an impressive 135 lbs/min (1,930 cfm). Stepping up to an S488 SX-E for all-out horsepower and race applications, you’re looking at a turbo that moves 160 lbs/min (2,285 cfm) and supports up to 1,575 hp according to BorgWarner. According to the aftermarket, however, 1,740 hp has been achieved with an S488 SX-E on the engine dyno.
While fitment of a BorgWarner S300 isn’t a bolt-in proposition for Duramax or Power Stroke owners (you’ll need a different mounting system), the S300SX3 line caters almost exclusively to common-rail Cummins applications. Right out of the box, a 60mm (68mm turbine), 63mm (68mm turbine), and 66mm (73mm turbine) S300SX3 equipped with a 90-degree compressor outlet cast into the compressor housing will directly replace the factory turbo, so long as the exhaust manifold has been changed or altered to accept BorgWarner’s T4 exhaust housing.
For ’94-’02 5.9L Cummins owners, BorgWarner makes a 100-percent drop-in replacement for the stock turbo (T3 divided exhaust housing and all) coined the S300GX. It features a cast 57mm inducer compressor wheel, a 64.5mm exducer turbine wheel, and comes standard with a .80 A/R T3 flange exhaust housing. Designed for lower horsepower second-gen applications but still capable of supporting north of 400-rwhp, it spools quick and has a reputation for durability.
When BorgWarner released its SX-E super-core line several years ago, the overall quality of its turbocharger package improved considerably. For example, all SX-E turbos come standard with a 360-degree thrust bearing, forged milled compressor wheel (FMW), and an optimized compressor housing. All super-cores must be spec’d with the exhaust housing of your choice (an added cost). In contrast, the older SX line of chargers came standard with a 270-degree thrust bearing assembly and a cast compressor wheel.
For an S300 frame turbo, the release of the S369 SX-E was big news when it hit the market. Its 69mm inducer FMW compressor wheel flows 98 lbs/min (1,400 cfm), which rivaled cast 75mm wheels at the time, and the inclusion of an integrated shaft speed sensor port and pre-machined boost monitoring port were additional selling points for what was then the hottest S300 on the market.
Released in 2018, BorgWarner’s S372 SX-E one-upped the 69mm version and once again proved how the company’s big wheeled S300’s contradicted some of the aftermarket chatter than its turbos were “too big” and hard to package. With its FMW compressor wheel capable of flowing 110 lbs/min (1,570 cfm), the S372 SX-E is designed to support big horsepower (as much as 1,100 hp in some applications) without having to upgrade to an S400 frame charger.
The well-established performance gains, durability, and versatility associated with S300 and S400 turbochargers has led to a myriad of S300 and S400 conversion kits in the aftermarket. No matter what model year Duramax you own, there is a system available to convert your LB7-L5P into a BorgWarner S300 or S400-fed beast. Here, you can see an S366 SX-E in the valley of an LBZ, made possible thanks to an S300 single install kit from HSP Diesel.
A reputation for durability, adjustable compressor and exhaust housing orientation, and an ability to provide solid performance gains prompted many aftermarket companies to build T4 turbo mounting kits for the 7.3L Power Stroke. By being able to run a T4 S300 or S400 BorgWarner, ’94.5-’03 Ford owners could move beyond factory-modified turbo options and slightly bigger yet air-limited replacements. S366 variants have proven capable of supporting more than 500-rwhp, with S400’s helping some 7.3L’s clear in excess of 700-rwhp.
S300 frame turbochargers found a home on the 6.0L Power Stroke when owners either became fed up with the engine’s rampant VGT issues, or sought more power. The 6.0L responds very well to the S362, the S363, and S366 turbos, and this type of swap (a T4 divided system) remains a solid choice for both reliability and performance. With the right injector, a 6.0L sporting an S366 can support 700-rwhp. The system shown here is built by Smeding Diesel.
The 6.4L Power Stroke is equally receptive to an S300 swap, and its displacement edge over the 6.0L allows it to drive smaller S400’s for Ford owners seeking big power. It’s also worth noting that ditching the factory compounds in favor of a single S300 or S400 relieves the strain the 6.4L engines typically see. Most notably, drive pressure is greatly reduced after the swap.
In the Cummins realm, S300’s seem to work best on 5.9L mills while S400’s fit the bill perfectly on the 6.7L. The larger displacement of the 6.7L Cummins allows it to spool an S400 much easier, even with factory injectors in the equation. In many applications, a smaller S400 is hardly less responsive at low rpm than the factory VGT. No different from the Duramax and Power Stroke applications previously listed, a completely new turbo system is required to swap an S400 onto a 6.7L Cummins, and a second-gen turbo swap kit from Fleece Performance Engineering is shown here.

The “S” in S300 and S400 Comes From Schwitzer

This was the naming system applied to all Schwitzer turbochargers when BorgWarner acquired the company and retained its nomenclature back in 1999. Coincidentally, this was also roughly the same time period in which BorgWarner purchased AG Kuhnle, Kopp & Kausch, and renamed that turbocharger line 3K-Warner (you may have heard some of BorgWarner’s K-series terminology before).


Another neat tidbit is that the S300 frame turbos are designed for engines between 7 and 11 liters in displacement, and S400’s are intended for 11 to 16 liter engine applications… It just goes to show you how much fueling and airflow is being sent through our engines, most of which displace half that size.

On ’11-’14 6.7L Power Strokes, engines plagued with factory turbo issues, an S300 or moderately sized S400 is right at home. Not only does a fixed geometry turbo simplify the overall system, but a properly sized charger will lower the drive pressure (i.e. stress) the 6.7L sees. For a solid balance in overall drivability, an S366 SX-E, S369 SX-E, or an S372 SX-E would be good choices from the S300 lineup, while an S467.7 or S472 SX-E would scratch any owner’s big single itch.
For years, S300 over S400 compound configurations have been common in the diesel industry, especially on Cummins applications. And thanks to BorgWarner offering so many S300 and S400 turbo options, the possibilities are virtually endless. Many owners who start out using an S362, S363, or S366 as a single on their 5.9L combine it with an S400 when the time comes to install compounds. The combination of an S362 over S475 on a 5.9L provides for a solid towing arrangement, with S364/S480 or larger turbos being more suited for all-out horsepower. A large S300 paired with an S488 SX-E or even a pair of S400’s work well for 6.7L Cummins owners with big horsepower goals in mind.
Beyond the fixed geometry, journal bearing S300 and S400 variants, BorgWarner has been on the leading edge of supplying variable geometry and unique compound turbocharger systems at the OEM level over the years. The company produced the series sequential turbo system that came factory on the 6.4L Power Stroke, for example. The compact compound arrangement coupled a 52mm compressor VGT with a 65mm low-pressure fixed geometry turbo, and in time the aftermarket discovered that the stock system could support 600-rwhp. For reference, most 6.4L Power Stroke-equipped ’08-’10 Super Duty’s made 290-rwhp from the factory.
In 2008 BorgWarner launched the first regulated two-stage turbo system, the R2S, with variable turbine geometry (VTG) for the M57 3.0L inline-six powering the BMW 335d. The innovative system paired a BorgWarner K39 high-pressure turbo with a K26 low-pressure unit, with the K26 essentially seeing zero exhaust flow in order to quickly bring the K39 up to full steam ahead. However, once up to operating speed a bypass valve begins to divert exhaust flow into the K26, but does so in a way that keeps the K39 humming along at full song. Long story short, this turbo package is highly efficient, rock-solid reliable, and they hold up fine at twice the factory boost and horsepower level.


BorgWarner Turbos

Fleece Performance Engineering

HSP Diesel

Pure Diesel Power

Scheid Diesel

Smeding Diesel

Summit Racing



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